Energy generated from wind through the use of large scale wind turbines has experienced rapid growth in recent years. Source of this growth may be the numerous environmental, technical and economic benefits related to wind generated energy production. Wind energy is widely available, renewable and reduces the production of greenhouse gases by diminishing the need of fossil fuels as energy source. Furthermore, improvements in design, manufacturing technologies, materials and power electronic devices of wind turbines has and will in the future continue to decrease production costs of wind turbines while increasing their energy production capabilities and efficiencies.
At least some known wind turbines include a tower and a nacelle mounted on the tower. A rotor is rotatably mounted to the nacelle and is coupled to generator by a shaft. A plurality of blades extend from the rotor. The blades are oriented such that wind passing over the blades turns the rotor and rotates the shaft, thereby driving the generators to generate electricity. The generators are sometimes, but not always, rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the rotor for the generator to efficiently convert the rotational mechanical energy to electrical energy, which is fed into a utility grid via at least one electrical connection. Gearless direct drive wind turbines also exist. The rotor, generator, gearbox and other components are typically mounted within a housing, or nacelle, that is positioned on top of a base that may be a truss or tubular tower.
The nacelle typically includes many power electronic devices that enable a controlled and efficient conversion of wind energy into electrical energy such as, for example, one or more generators, control and cooling systems, and so forth. The power and control cables for these devices, and well as the cables that feed electrical power into electrical supply grids, are routed from the nacelle into the tower where they initially hang free in a “drip loop” section of the tower in order to twist during rotation of the nacelle.
To maximize the energy production of a wind turbine, the nacelle is typically able to rotate or pivot versus the fixed position of the tower. This allows the rotor blades to be in an optimum position with respect to the wind direction. Equally, to avoid unfavorable wind gusts or extremely high wind speeds, the position of the nacelle may be adjusted accordingly. Based on this rotational movement of the nacelle, the cables in the drip loop section may be pulled together in a kind of uncontrolled “knurl”, which is considered as an aggregation of at least one cable, for example, in the form of a cable knot that results from twist, strain, or writhe of the cable. Twisting forces of the nacelle may cause the cable to coil-up or super-coil and thus get pulled together, hence, usually shortening the relative length and broadening the relative width of the cable at the aggregation site. Generally, one twist is equivalent to one complete rotation of the cable around its longitudinal axis, hence one 360 degree rotation.
The twisting and curling behavior of the cables during operation of a wind turbine may lead to several disadvantageous issues, such as overheating in the knurls or movement of the knurls to other parts in the tower such as, for example, the ladder or lights. Further, the movement of the knurl may cause excessive wear of the cables or may damage surrounding structures. In the worst case, such uncontrolled movements of the cable knurls may result in entanglement of the cables inside of the tower that may eventually lead to system failure.
In a conventional configuration, a metal surrounds the cables in the drip loop section and is fixed to the tower wall via an elongated bracket. However, since the cables move vertically and laterally during operation of the wind turbine, this metal ring may cause abrasion of the cables.
Thus, it is appreciated in the industry that controlling the cable knurls is beneficial. To this end, U.S. Pat. No. 8,366,396 proposes a cable drip loop securement system that prevents knurl formations beyond a specified area of at least one cable that is routed from the nacelle into the tower. The securement system includes a displaceable cable drip loop securement device that accommodates part of the cable and a positioning element for connecting the cable loop securement device inside of the tower. The cable can turn and eventually form knurls only above the cable loop securement device.
Thus, the industry is continuously seeking improved systems and devices for controlling the cables from the nacelle in the tower that address at least certain of the issues noted above.